| 1. |
Understand
the purpose of dimensions
See textbook pages
332-345
After an object has been drawn
correctly it must be dimensioned in order for it to be built to the
correct size.
Dimensioning standards will vary
from office to office and discipline to discipline, but dimensioning
follows general guidelines.
Some offices adhere to a National
Standard known as ANSI (American National Standard Institute). These are
generally manufacturing companies that need to work to high tolerances.
The following is a guideline which you will use in this course:
|
B12
Reading Chapter only |
| 2. |
Horizontal
Dimensions
Horizontal dimensions should be
placed in plan view, except when better recognized somewhere else.
|
|
| 3. |
Dimension
Placement from object
Dimension line placement from an object should be
3cm (1-1/2").
Parallel dimension placement should be 1cm (3/8").
|
|
| 4. |
Dimensioning
Diameters
See textbook pages
346-347 "Dimensioning
& Notes for size features"Diameter leader line should be directed to pass through the center of the
circle but should actually stop at the outside of the circle itself. The text,
leader and vertical, but always on an angle.
|
|
| 5. |
Dimensioning
Radius
Radius leader line should go through the center of the arc. Text and leader should be placed outside of the arc and arrow should be inside of the arc.
|
|
| 6. |
Identify
Centerlines
Centerline notation should always be directly on the centerline. Never notate a centerline with a leader.
|
|
| 7. |
Placement
relative to object
See textbook page
351-353
Dimensions and notes should be placed outside of the object. The dimension should be placed inside the object only as a last resort.
|
|
| 8. |
Placement
in multiple views
Dimensions should be applied to one view only, and it should be the view
that shows the distance in its true length.
|
|
| 9. |
Place
smaller dimensions first
Always place longer dimension lines outside of the shorter ones. This will not only delete the possibility of crossing dimensions, but it will ensure
the overall dimension (size of object) be outside all other dimensions.
|
|
| 10. |
Dimensioning
to a center line
Use extended center line instead of an extension line to dimension
to a center line.
Centerlines should only be placed
on an object if you are going to use it to dimension to or for location
purposes. Centerlines should also only be placed on fabrication
drawings as that is where the detail would be dimensioned.
|
|
| 11. |
Crossing
of lines
Never allow the crossing of two dimension lines or an extension line and
a dimension line, unless absolutely necessary.
If you must, always break the
extension line and never the dimension line.
NOTE: It is allowable to let two extension lines cross
|
|
| 12. |
Dimensioning
Holes
Drilled, reamed, bored, punched, cored holes, etc. are usually specified
by a note giving the diameter, operation and depth if required.
If there is more
than one hole of the same kind, the leader needs to point
to one hole only and the number
of holes is stated.
|
|
| 13. |
Dashed
lines
Avoid dimensioning to dashed lines and object lines if possible.
NOTE: In the case below it would be better to dimension to the hole in the
plan view instead of the to the dashed line.
|
|
| 14. |
Dimensions
before annotations
Always dimension the object first, (lengths, widths, depth, etc.) then do
all notations.
Because a note can be placed on the
drawing with a leader line, it has
a little more freedom than an object dimension.
 |
|
| 15. |
Properties of a Dimension
Notice the extension line extends past the dimension line.
The extension line should
|
|
| 16. |
Dimension
Styles
|
|
| 17. |
Preferred
Dimensioning Practices See
Dimensioning for Mechanical Notes (Belt Conveyors)
|
|
| |
|
|
